Geological Time Scale 
                                                                  
                Component-I(A) - Personal Details 
                Role                             Name                                  Affiliation 
                Principal Investigator           Prof. Masood Ahsan Siddiqui           JamiaMilliaIslamia, 
                                                                                       New Delhi 
                Paper Coordinator, if any        Dr.SayedZaheenAlam                    Dyal Singh College, 
                                                                                       University of Delhi, New 
                                                                                       Delhi 
                Content Writer/Author (CW)  Dr. Shadab khan                            Department of 
                                                                                       Geography, 
                                                                                       Kirori Mal College 
                Content Reviewer (CR)            Dr.SayedZaheenAlam                    Dyal Singh College, 
                                                                                       University of Delhi, New 
                                                                                       Delhi 
                Language Editor (LE)                                                    
                         
                Component-I (B) - Description of Module 
                 Items                             Description of Module 
                 Subject Name                      Geography 
                 Paper Name                        Geomorphology   
                 Module Name/Title                 Geological Time Scale   
                 Module Id 
                                                   GEO- 3 
                 Pre-requisites                    Nature     and     Development       of    Geomorphology, 
                                                   Continental Drift Theory, Mountain Building 
                 Objectives                        To  know  about  the  Geological  time  scale  and  its 
                                                   different  era  like  Precambrian,  Palaeozoic,  Mesozoic 
                                                   and Cenozoic. 
                 Keywords                          Geological time, Eras, Periods, Precambrian, 
                                                   Palaeozoic, Mesozoic,  Cenozoic, Carboniferous, 
                                                   Cambrian  , Devonian , Silurian, Quaternary Period, 
                                                   and  Holocene 
                 
                 
                 
                 
        
        
        
        
                      Geological Time Scale 
        
       Life on the earth did not come into being with its birth.  The earth has a long history and has 
       seen  many  changes  on  her  surface  through  different  periods.  The  earth  cooled  from  its 
       gaseous state into liquid one and transformed into solid layer on further cooling. For an 
       instance, there was a great ocean in place of the Himalayas only 150 million years back.With 
       one cellular organism, life beganwhich belonged to both animal and vegetation kingdom. 
       Later  on,  the  animals  and  vegetations  both  evolved  into  more  complex  life-forms.  The 
       animals evolved into fish, reptiles, mammals and finally into human beings. The great age of 
       the earth were based on the rate of sedimentation, age of fossils, and the rate of cooling of the 
       earth,salinity of the oceans and the tidal force of the moon.As far as,the age of the Earth is 
       concerned,there is a lot of difference of opinion among the scientists.On the basis of current 
       methods of radio-metric dating, most of the modern scientists agree that the life of the Earth 
       may range from 3 to 5 billion years.  
        
       James Hutton believed in the principle of uniformitarianism and he knew that the earth was 
       very old but they had no method of knowing its exact age. Several methods were devised by 
       others which were in use till about the beginning of the 20th century.Lord Kelvin (in 1897), a 
       renowned physicist, had assumption that the earth was originally molten and cooled to its 
       present condition, put the earth’s age  at not more than 100 million years, and perhaps much 
       less.  
        
                                                  
       Rutherford,  (in  1904)  for  the  first  time  took  the  help  of  radioactive  substances  in 
       determining  the  age  of  the  earth.    For  calculating  the  ages  of  rocks  and  minerals,  the 
       discovery of radio-activity provided a reliable means; contain radioactive isotopes (elements). 
       This  method  is  called  radiometric  dating.  Till  about  40  years  ago  the  age  of  the  earth 
       calculated on this basis was placed at about 3,000 million years. In recent years, it has been 
       possible to make more accurate calculations due to more precise scientific knowledge.The 
        
                        
                       relative percentage of lead isotopes in ancient rocks and meteorites has also been taken into 
                       account and the age of the earth is now placed at around 4,600 million years. Chances of 
                       error in this calculation are very small;therefore this age is now widely accepted. 
                        
                        
                        
                       Geological History of the Earth 
                       Though life on earth has existed only for a small fraction of her history, fossils, which are 
                       remains of extinct animals, indicate a good deal. It is possible to estimate the depth of the sea 
                       on the basis of fossils of certain marine animals like corals, where particular sediment was 
                       precipitated.Furthermore  fossils  provided  indications  of  past  environments.  Radiometric 
                       dating has made possible the specific or absolute dating of rock units that represent various 
                       events in the earth's distant past. When a complete sequence of rocks representing the entire 
                       period  is  not  available  and  there  are  breaks  in  the  rock  record,  then  it  is  known 
                       unconformities.  
                       The principal divisions of geological time are called eras. Three eras are recognised- the 
                       Plaeozoic (ancient life), the Mesozoic  (middle life) and the Cenozoic (recent life). Each 
                       of these eras is subdivided into smaller time units known as periods. 
                       The  Palaeozoic  has  seven  periods,Mesozoic    and  Cenozoic  has  three  andtwo  periods 
                       respectively.  Each  period  is  characterized  by  its  profound  changes  in  life  forms.  These  
                       twelve periods is further sub-divided into epochs and epoch into ages.  
                       It  will  be  observed  that  the  Palaeozoic  era  begins  some  600  million  years  ago.  The 
                       enormously long period of more than 4 billion years prior to the Pre-cambrian with no further 
                       subdivision, as our knowledge about those early times is very limited. This is so, because 
                       prior to the Cambrian, very simple life forms such as algae, bacteria, fungi, sponges and 
                       worms have not left adequate fossil record.On the basis of the above discussion a standard 
                       geological timescale has been prepared which is accepted throughout the world and with 
                       reference to which the geological history of the earth can be studied.  
                                                                              Stratigraphic Chart 
                      Era                 Period                        Epoch                      Million              Distinctive Life             Major 
                                                                                                  YearsAge                                           Structural 
                                                                                                                                                     Episodes 
                      Cenozoic            Quaternary                    Recent/ Holocene          0.01                  Ice age ends                  
                                                                                                                        Humans are dominant 
                                                                        Pleistocene/              2.5                   Age of Man                   Main            Alpine 
                                                                        more recent                                                                  Episode 
                                          Tertiary                      Pliocene                  12                    Age of mammals-               
                                                                        Miocene                   25                    (flowering plants and         
                                                                        Oligocene                 35-40                 broad leaved trees)          Laramide Phase 
                                                                        Eocene                    60                                                  
                                                                        Paleocene                 70                                                  
                      Mesozoic            Cretaceous                                              135                   Age       of      reptiles   General  Worldwide 
                                          (Creta=chalk)                                                                 (Dinosaurs) and birds        Elevation 
                                          Jurassic(after       Jura                               180                                                 
                                          mountain) 
                                          Triassic    (three    fold                              225                                                 
                                          division in Germany) 
                      Palaeozoic          Permian                                                 270                   Age of Amphibians            Main        Hercynian 
                                                                                                                                                     Episode 
                        
                       
                                       Carboniferous                                        350                Widespread forests           
                                       Devonian                                             440+101            Age of fishes                
                                       Silurian                                             440+10             Age of marine                
                                       Ordovician                                           500                Invertebrates                
                                       Cambrian                                             600                Abundant  fossils  first    Main      Caledonian 
                                                                                                               appear                      Episode 
                     Azoic        or                                                        Oldest    rocks                                Several     Mountain 
                     Precambrian                                                            3787+85                                        Building Episodes 
                      Source: Dayal, P. “A Textbook of Geomorphology”, Shukla book depot, Patna, 1994 & 
                      https://andyckh.deviantart.com/art/Geological-Timeline-Chart-283922560 
                      It is clear from the above table that man is comparatively a new comer on the Earth. Even this 
                      history of the earth constitutes not more than one sixth of the life of the earth, nothing is 
                      known about 5/6th of the Earth's history. 
                      Source: https://abstractgeology.files.wordpress.com/2012/10/geological-time.jpeg 
                       
                      Division of Geological Time into Eras 
                      We have noticed above that geological time has been divided into four major divisions called 
                      eras-Precambrian, Palaeozoic, Mesozoic and Cainozoic or Cenozoic. The oldest and by far